Acrylonitrile polymer composition stabilized with the zinc reduction product of methylol sulfonic acid and method of making same



Lloyd T. Jenkins, Decatur, Ala., assignor to The Chemstrand Corporation, Decatur, Ala., a corporation of Delaware Application December 17, 1956 Serial No. 628,490

17 Claims. (Cl. 260--30.4)

No Drawing.

This invention relates to the stabilization of acrylonitrile polymers and blends thereof. More particularly, it relates to the stabilization of acrylonitrile polymers and blends thereof which have a tendency to develop color upon standing or application of heat.

The term polymer, as employed in the instant description and claims, is intended to include homopolymers, copolymers, and blends thereof, said polymers containing at least 80 percent by weight of polymerized or copolymerized acrylonitrile in the polymer molecule.

Acrylonitrile polymers containing 80 percent or more of acrylonitrile are generally insoluble in the more common solvents and in those instances where suitable'solvents have been found, in order to effect solution, the application of heat is usually necessary. Where heat is employed to effect solutions, from which shaped articles are to be formed, a tan to dark brown color frequently develops in the solutions and therefore is carried over into the product formed therefrom. This color also develops in solutions upon standing for prolonged periods of time.

The mechanism which causes color formation has not been definitely ascertained, although a variety of reasons therefor have been advanced. The presence of metal ions, such as iron, copper and manganese in the solutions may cause the color. The employmentof amide compounds as solvents may result in formation of amines when heat is applied and cause color in the compositions. Impurities present in the solvents have also been cited as a cause. Whatever may be the reason for color formation, it results in compositions andproducts of undesirable standards and therefore, has been the source of con cern, particularly in commercial operations where such types of polymers or copolymers are employed.

, Accordingly, it is an object of the present invention to prevent undesirable color formation in acrylonitrile polymer compositions.

Another object is to minimize color formation when solutions of the acrylonitrile polymers are permitted to stand for a prolonged period of time or upon application of heat.

It is also an object of the invention to prevent color formation in acrylonitrile polymers at elevated temperatures.

A still further object of the invention is the production of solutions ofacrylonitrile polymers and articles produced therefrom having improved color characteristics. Other objects and advantages will be apparent from a consideration of the description of the invention which follows hereafter.

In general, the objects of the invention are'accomplished by dissolving the polymer of acrylonitrile in a suitable solvent therefor, and preventing or minimizing color formation by the presence in the solution as an United States Patent tent of at least 80 percent by weight.

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inhibiting agent, the zinc reduction product of methylol sulfonic acid. Y

The zinc reduction product of methylol sulfonic acid is a mixture of methylol sulfonic acid, methylol sillfinic acid, formaldehyde, zinc formaldehyde sulfoxylate and basic zinc formaldehyde sulfoxylate. The product is prepared by bubbling an equimolar amount of sulphur dioxide through 600 milliliters of an aqueous solution containing 37 percent formaldehyde. The reduction is exothermic and the temperature rises to about or C. and then slowly decreases to room temperature when the reaction is substantially complete. The methylol sulfonic acid resulting from this reaction is then reduced by adding zinc dust directly to the solution while stirring at such a rate asto maintain the temperature at 50 C. However, the temperature at which the Zinc reduction takes place is not critical. After 3 to 4 hours the reduction is complete. The temperature is allowed to decrease to about 25 C. and the excess zinc dust is then filtered ofi. If desired, this product may be stored in closed containers to prevent air oxidation until ready for use. The zinc reduction product of methylol sulfonic acid is an excellent color inhibitor. Polymer dopes, or fibers spun therefrom, which contain this product, have no objectionable odor which is often true when many of the well-known color inhibitors are employed.

It has also been found that the product does not cause a precipitate to form in the spin bath solution and thereby clog the apertures of the spinneret when wet-spinning polymer dopes in which it is contained. The clogging of the apertures, of the spinneret and the precipitate in the spin bath create a necessary shut down of the spinning lines when many of the well-known color inhibitors are emp dt The total amount of inhibiting agent may be employed in a range of about 0.3 to 15 percent based on the total polymer weight. However, it is preferred that the inhibiting agent of. theinstant invention be present in a small amount compared to the amount of polymer dissolved. Thus, although the amount is not critical it is preferred that the inhibiting agent be present in the amount of about 0.3 to 3.0 percent based on the total weightof the polymer. The inhibiting agent may be added to the solvent before or after the polymer is dissolved therein. The inhibiting agent permits exposure at high temperaures for prolonged standing periods without the development of the objectionable colorwhich usually results in such solutions. The compositions of the instant invention may be prepared in a varying temperature range. For example, the compositions of the instant invention may be prepared by mixing the polymer, a suitable solvent and the inhibiting agent at any temperature or heating the mixture at a temperature up to the boiling point of the solvent.

Among the solvents which maybe used in practising the instant invention are N,N-dimethylformarnide, N,N- dimethylacetamide, aqueous zinc chloride, sulfuric acid, aqueous nitric acid, aqueous sodium thiocyanate, ethyl ene carbonate, sulfolane, nitromethane and the like.

The polymeric materials, which may be employed in the practice of the present invention, are polyacrylonitrile, copolymers, including binary and ternary polymers containing at least 80' percent by weight of acrylonitrile in the polymer molecule, or a blend comprising polyacrylonitrileor copolymers comprising acrylonitrile with from 2 to 50 percent of another polymeric material, the blend having an overall polymerized acrylonitrile con- While the preferred polymers employed in the instant invention are those containing at least 80 percent of acrylonitrile, generally recognized as the fiber-forming acrylonitrile poly mers, it will be understood that the invention is likewise applicable to polymers containing less than 80 percent acrylonitrile and the same stability is realized with the inhibiting agents defined herein. The acrylonitrile polymers containing less than 80 percent acrylonitrile are useful in forming films, coating cmpositions, molding operations, lacquers, and the like, in all of which applicatons the alleviation of undesirable color is extremely important.

For example, the polymer may be a copolymer of from 80 to 98 percent acrylonitrile and from 2 to 20 percent of another monomer containing the C=C linkage and copolymerizable with acrylonitrile. Suitable mono-.olefinic monomers include acrylic, alpha-chloroacrylic and methacrylic acids; the acrylates, such as methylmethacrylate, ethylmethacrylate, butylmethacrylate, methoxymethyl methacrylate, beta-chloroethyl methacrylate, and the corresponding esters of acrylic and alphachloroacrylic acids; vinyl chloride, vinyl fluoride, vinyl bromide, vinylidene chloride, l-chloro-l-bromoethylene; methacrylonitrile; acrylamide and methacrylamide; alphachloroacrylamide, or monoalkyl substitution products thereof; methyl vinyl ketone; vinyl carboxylates, such as vinyl acetate, vinyl chloroacetate, vinyl propionate, and vinyl stearate; N-vinylimides, such as N-vinylphthalimide and N-vinylsuccinimide; methylene malonic esters; itaconic acid and itaconic ester; N-vinylcarbazole; vinyl furane; alkyl vinyl esters; vinyl sulfonic acid; ethylene alpha, beta-dicarboxylic acids or their anhydrides or derivatives, such as diethylcitraconate, diethylmesaconate, styrene; vinyl naphthalene; vinyl-substituted tertiary heterocyclic amines, such as the vinylpyridines and alkyl-substituted vinylpyridines, for example, 2-vinylpyridine, 4-vinyl-pyridine, 2-methyl-5-vinylpyridine, etc.; l-vinylimidazole and alkyl-substituted l-vinylimidazoles, such as 2-, 4-, or S-methyl-l-vinylimidazole, and other C=C containing polymerizable materials.

The polymer may be a ternary interpolymer, for example, products obtained by the interpolymerization of acrylonitrile and two or more of any of the monomers, other than acrylonitrile, enumerated above. More specifically, and preferably, the ternary polymer comprises acrylonitrile, methacrylonitrile, and 2-vinylpyridine. The ternary polymers preferably contain from 80 to 97 percent of acrylonitrile, from 1 to percent of a vinylpyridine or a l-vinylimidazole, and from 1 to 18 percent of another substance, such as methacrylonitrile or vinyl chloride.

The polymer may also be a blend of polyacrylonitrile or of a binary interpolymer of from 80 to. 99 percent acrylonitrile and from 1 to 20 percent of at least one other C=C containing substance with from 2 to 50 percent of the weight of the blend of a copolymer of from 10 to 70 percent of acrylonitrile and from 30 to 90 percent of atleast one other C=C containing polymerizable monomer. Preferably, when the polymeric material comprises a blend, it will be a blend of a copolymer of 90 to 98 percent acrylonitrile and from 2 to 10 percent of another mono-olefinic monomer, such as vinyl acetate, which is not receptive to dyestuif, with a sufiicient amount of a copolymer of from 10 to 70 percent of acrylonitrile and from 30 to 90 percent of a vinyl-substituted tertiary heterocyclic amine, such as vinylpyridine or l-vinyl-imidazole, to give a dyeable blend having an overall vinyl-substituted tertiary heterocyclic amine content of from 2 to 10 percent, based on the weight of the blend.

The polymers, useful in the practice of the present invention, may be prepared by any conventional polymerization procedure, such as mass polymerization methods, solution polymerization methods, or aqueous emulsion procedures. However, the preferred practice utilizes suspension polymerization wherein the polymer is prepared in finely divided form for immediate use in the fiber fabrication operations. The preferred suspension polymerization may utilize batch procedures, wherein monomers are charged with an aqueous medium containing the necessary catalyst and dispersing agents. A more desirable method involves the semi-continuous procedure in which the polymerization reactor containing the aqueous medium is charged with the desired monomers and the continuous withdrawal of polymer may also be employed.

The polymerization is catalyzed by means of any Watersoluble peroxy compound, for example, the potassium, ammonium and other water-soluble salts of peroxy acids, sodium peroxide, hydrogen peroxide, sodium perborate, the sodium salts of other peroxy acids, and any other water-soluble compound containing a peroxy group (-OO). A wide variation in the quantity of peroxy compound is possible. For example, from 0.1 to 3.0 percent by Weight of the polymerizable monomer may be used. The catalyst may be charged at the outset of the reaction, or it may be added continuously or in increments throughout the reaction for the purpose of maintaining a more uniform concentration of catalyst in the reaction mass. The latter method is preferred because it tends to make the resultant polymer more uniform in its chemical and physical properties.

Although the uniform distribution of the reactants throughout the reaction mass can be achieved by vigorous agitation, it is generally desirable to promote the uniform distribution of reagents by using inert Wetting agents, or emulsion stabilizers. Suitable reagents for thispurpose are the water-soluble salts of fatty acids, such as sodium oleate and potassium stearate, mixtures of water-soluble fatty acid salts, such as common soaps prepared by the saponification of animal and vegetable oils, the amino soaps, such as salts of triethanolamine and dodecylmethylamine, salts of rosin acids and mixtures thereof, the water-soluble salts of half esters of sulfuric acid and long chain aliphatic alcohols, sulfonated hydrocarbons, such as alkyl aryl sulfonates, and any other of a wide variety of wetting agents, which are in general organic compounds containing both hydrophobic and hydrophilic radicals. The quantity of emulsifying agents will depend upon the particular agents selected, the ratio of monomer to be used, and the conditions of polymerization. In general, however, from 0.01 to 1.0 percent by weight of the monomers may be employed.

The emulsion polymerizations are preferably conducted in glass or glass-lined vessels which are provided with a means for agitating the contents. Generally, rotary'stirring devices are the most effective means of insuring the intimate contact of the reagents, but other methods may be successfully employed, for example, by rocking or tumbling the reactors. The polymerization equipment generally used is conventional in the art and the adaptation of a particular type of apparatus to the reaction contemplated is within the province of one skilled in the art. The articles manufactured therefrom may be produced by well-known conventional methods, for example,

the Wet-spinning, dry-spinning and melt-spinning methods for producing fibers.

The following examples are illustrative rather than limitative and all parts, proportions and percentages are by weight unless otherwise specified.

EXAMPLE I 7.5 grams of a polymer blend of 88 percent of a copolymer containing 94 percent acrylonitrile and 6 percent of vinyl acetate and 12 percent of a copolymer of 50 percent of acrylonitrile and 50 percent of 2-methyl-5-vinyl pyridine were added to 45 milliliters of N,N-dimethylacetamide containing approximately 0.05 gram of titanium dioxide. The mixture was stirred and heated for 50 minutes at 90 C. It was then quickly cooled to :room temperature and the color measured. This sample was added hereto. The purity is set forth below.

Table I Inhibitor Percentage Purity Used Control 10.7 Zinc Reduction Product of M th lol Sulfonic Acid- EXAMPLE ii 7.5 grams of a copolymer containing 90 percent of 1 Table II Inhibitor Percentage Purity Used Control 12. 7 Zinc Reduction Produ t of Methylol Sulfonic Acid 1 6. 4

EXAMPLE III 7.5 grams of an acrylonitrile homopolymer were added to 45 milliliters of N,N-dimethylacetamide containing approximately 0.05 gram of titanium dioxide. The mixture was stirred and heated for 50 minutes at 90 C. It was then quickly cooled to room temperature and the color measured. This sample was used as a control. The purity of the control sample is set forth below. Subsequently, like samples were prepared but with 0.075 gram of the zinc reduction product of methylol sulfonic acid added thereto. The purity is set forth below.

Table III Inhibitor Percentage Purity Used Control 13. 5 Zinc Reduction Product of Methylol Sulfonlc Acid 1 10.0

The tests for color indicative of approaching whiteness used throughout the examples consist of measurements of purity as calculated from the tristimulus values determined on a General Electric Spectrophotometer by the methods recommended by the Standard Observer and Coordinate System of the International Commission on Illumination, as fully set forth in the Handbook of Colorimetry published by The Technology Press, Massachusetts Institute of Technology in 1936.

The compositions of the instant invention present many advantages. For example, products formed from the polymer solutions of the instant invention are free of objectionable color and therefore of greater commercial value. In preparing the polymer solutions, heat may be applied without the danger of color formation and the solutions, if necessary, may stand for prolonged periods and remain free of color. The inhibiting agents are readily available and inexpensive. Therefore, no great increase in production cost is necessary. The compositions containing the inhibitors may be prepared without going through detailed and elaborate procedures that 6 necessitate expensive changes in the design of the apparatus used to manufacture them.

It will be understood to those skilled in the art that many apparently widely different embodiments of this invention can be made without departing from the spirit and scope thereof. Accordingly, it is to be understood that this invention is not to be limited in the specific embodiments thereof except as defined in the appended claims.

, I claim:

l. A new composition of matter comprising apolymer containing at least percent of polymerized acrylonitrile and up to 20 percent of another polymerizable mono-olefinic monomer copolymerizable therewith, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of the zinc reduction product of methylol sulfonic acid prepared by passing an equimolar amount of sulfur dioxide through an aqueous solution containing 37 percent formaldehyde, and thereafter reducing the solution with an excess of :zinc dust.

2. A new composition of matter as defined in claim 1 wherein the polymer is a copolymer containing 80 to 98 percent of acrylonitrile and 2 to 20 percent of a polymerizable mono-olefinic monomer copolymerizable therewith.

3. A new composition of matter as defined in claim 1 wherein the polymer is a blend of 80 to 99 percent of (A) a copolymer containing to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate and l to 20 percent of (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30 to 90 percent of Z-methyl- 5-vinyl pyridine.

4. A new composition of matter as defined in claim 1 wherein the polymer is polyaorylonitrile.

5. A new composition of matter as defined in claim 1 wherein the solvent is N,N-dimethylacetamide.

6. A new composition of matter as defined in claim 1 wherein the solvent is N,N-dimethylformamide.

7. A new composition of matteras defined in claim 1 wherein the solvent is ethylene carbonate.

8. A new composition of matter as defined in claim 1 wherein the solvent is nitromethane.

9. A new composition of matter comprising a polymer blend of (A) a copolymer containing 90 to 98 percent of acrylonitrile and 2 to 10 percent of another polymerizable mono-olefinic monomer and (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30 to 90 percent of a vinyl-substituted tertiary heterocyclic amine, said blend having an overall vinyl-substituted tertiary heterocyclic amine content of from 2 to 10 percent, based on the weight of the blend, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of the zinc reduction product of methylol sulfonic acid prepared by passing an equimolar amount of sulfur dioxide through an aqueous solution containing 37 percent formaldehyde and thereafter reducing the solution with an excess of zinc dust.

10. A method for preparing a new composition of matter comprising mixing a polymer containing at least 80 percent of polymerized acrylonitrile and up to 20 percent of another polymerizable mono-olefinic monomer copolymerizable therewith, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of the zinc reduction product of methylol sulfonic acid prepared by passing an equimolar amount of sulfur dioxide through an aqueous solution containing 37 percent formaldehyde and thereafter reducing the solution with an excess of zinc dust; and heating the mixture to form a homogeneous solution.

11. The method as defined in claim 10 wherein the polymer is a copolymer containing from 80 to 98 percent of acrylonitrile and from 2 to 20 percent of another polymerizable mono-olefinic monomer copolymerizable therewith.

12. The method as defined in claim 10 wherein the polymer is a blend of 80 to 99 percent of (A) a copolymer containing 90 to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to percent of (B) a copolymer containing 10 to percent of acrylonitrile and 30 to 90 percent of 2-methyl-5-vinylpyridine.

13. The method as defined in claim 10 wherein the polymer is polyacrylonitrile.

14. The method as defined in claim 10 wherein the solvent is N,N-dimethylacetamide.

15. The method as defined in claim 10 wherein the solvent is N,l I-dirnethylformamide.

16. The method as defined in solvent is ethylene carbonate. 7

17. A method for preparing a new composition of matter comprising mixing a polymer blend of to 99 percent of (A) a copolymer containing to 98 percent of .acrylonitrile and 2' to 10 percent of vinyl acetate and 1 to 20 percent of (B) a copolymer containing 10 claim 10 wherein the to 70 percent of acrylonitrile and 30 to 90 percent of Z-methyl-S-vinylpyridine, N,N-dimethylacetamide, and 0.3 to 15 percent, based on the total weight of the polymer, of the zinc reduction product of methylol sulfonic acid prepared by passing an equimolar amount of sulfur dioxide through an aqueous solution containing 37 percent formaldehyde, and thereafter reducing the solution with an excess of zinc dust; and heating the mixture to a temperature in a range of 25 C. to the boiling point of said mixture to form a monogeneous solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,502,030 Scheiderbauer Mar. 28, 1950 2,560,694 Howard July 17, 1951 FOREIGN PATENTS 1,027,445 France May 12, 1953 

1. A NEW COMPOSITION OF MATTER COMPRISING A POLYMER CONTAINING AT LEAST 80 PERCENT OF POLYMERIZED ACRYLONITRILE AND UP TO 20 PERCENT OF ANOTHER POLYMERIZABLE MONO-OLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, A SOLVENT THEREFOR, AND 0.3 TO 15 PERCENT BASED ON THE TOTAL WEIGHT OF THE POLYMER, OF THE ZINC REDUCTION PRODUCT OF METHYLOL SULFONIC ACID PREPARED BY PASSING AN EQUIMOLAR AMOUNT OF SULFUR DIOXIDE THROUGH AN AQUEOUS SOLUTION CONTAINING 37 PERCENT FORMALDEHYDE, AND THEREAFTER REDUCING THE SOLUTION WITH AN EXCESS OF ZINC DUST. 